As the method for production of VCR, there is known, in JP-B-1974-17666 (patent Literature 1) and JP-B-1974-17667 (Patent Literature 2), a method which comprises subjecting 1,3-butadiene to cis-1,4 polymerization in an inert organic solvent using a catalyst obtained from water, a soluble cobalt compound and an organic aluminum chloride represented by the general formula AlRnX3-n and then, in the polymerization system, subjecting 1,3-butadiene to syndiotactic-1,2 polymerization in the presence of a syndiotactic-1,2 polymerization catalyst obtained from a soluble cobalt compound, an organic aluminum compound represented by the general formula AlR3 and carbon disulfide.
Also, as the method for production of VCR, there is described, in JP-B-1987-171 (Patent Literature 3), JP-B-1988-36324 (Patent Literature 4), JP-B-1990-37927 (Patent Literature 5), JP-B-1990-38081 (Patent Literature 6) and JP-B-1991-63566 (Patent Literature 7), for example, a method which comprises subjecting 1,3-butadiene to cis-1,4 polymerization in the presence or absence of carbon disulfide to produce a VCR, or, after production of the VCR, separating 1,3-butadiene from carbon disulfide for recovery and circulating 1,3-butadiene containing substantially no carbon disulfide and an inert organic solvent. Further, in JP-B-1992-48815 (Patent Literature 8), there is described a VCR which is small in die swell ratio when made into a compound and, when the compound has been vulcanized, is excellent in tensile stress and flex-cracking resistance and is suitable as a side wall of tire.
In JP-A-2000-44633 (Patent Literature 9), there is provided a method for producing a novel VCR, which comprises subjecting 1,3-butadiene to cis-1,4 polymerization in an inert organic solvent composed mainly of a C4 fraction, using a catalyst system comprising a halogen-containing organic aluminum compound, a soluble cobalt compound and water and, in the resulting polymerization reaction mixture, subjecting 1,3-butadiene to syndiotactic-1,2 polymerization in the presence of a syndiotactic-1,2 polymerization catalyst obtained from a soluble cobalt compound, a trialkyl aluminum compound and carbon disulfide. It is further disclosed that the VCR obtained is a VCR composition comprising 3 to 30% by weight of a boiling n-hexane-insoluble matter, which is a syndiotactic-1,2-polybutadiene having a form of dispersed short fiber crystals, and 97 to 70% by weight of a boiling n-hexane-soluble matter, which has a cis structure containing 90% or more of a cis-1,4-polybutadiene.
In JP-A-2000-154215 (Patent Literature 10) and JP-A-2000-159836 (Patent Literature 11), there is provided a method for producing a novel VCR, which comprises subjecting 1,3-butadiene to cis-1,4 polymerization using a catalyst obtained from (A) a metallocene type complex of a transition metal compound and (B) an ionic compound between non-coordinating anion and cation and/or an aluminoxane and, in the resulting polymerization reaction mixture, subjecting 1,3-butadiene to syndiotactic-1,2 polymerization in the presence of a catalyst obtained from at least one compound selected from (E) a cobalt compound, (F) an isocyanic acid compound and carbon disulfide.
In the syndiotactic-1,2 polymerization of 1,3-butadiene, however, there are cases that offensive odor derived from the sulfur compound used is generated depending upon the polymerization conditions employed, and improvement has been desired.
In U.S. Pat. No. 6,956,093 (Patent Literature 12), there is disclosed a method for producing a rubber composition of reduced odor, which comprises treating, with hydrogen peroxide, a syndiotactic-1,2-polybutadiene obtained by using a catalyst containing carbon disulfide as a catalyst component. However, the method is not preferred because the hydrogen peroxide may oxidize the double bond of the polybutadiene or the remaining butadiene monomer.
Patent Literature 1: JP-B-1974-17666
Patent Literature 2: JP-B-1974-17667
Patent Literature 3: JP-B-1987-171
Patent Literature 4: JP-B-1988-36324
Patent Literature 5: JP-B-1990-37927
Patent Literature 6: JP-B-1990-38081
Patent Literature 7: JP-B-1991-63566
Patent Literature 8: JP-B-1992-48815
Patent Literature 9: JP-A-2000-44633
Patent Literature 10: JP-A-2000-154215
Patent Literature 11: JP-B-2000-159836
Patent Literature 12: U.S. Pat. No. 6,956,093